The present invention relates to the generation of electric power from wind driven or other variable speed fluid driven turbines.
There are various means to transfer the power generated by variable speed turbines to a utility electric grid. AC-DC conversion of a directly coupled generator allows more power to be generated when the wind blows harder.
However, as this method is proportionately much more expensive for very large turbines, it has been preferable to deploy direct energy feed to the electric grid, by running the generator at constant speed. However, since winds speed vary, and turbine speeds are mismatched to generator speeds; in practice, a gear transmission is deployed between the wind turbine and the generator drive train to match the generator speed to achieve the grid frequency. To maintain the generator speed to a fixed value turbine speed control is achieved by rotating the airfoils to reduce the angle of attack as the wind speed increases. Both methods have their own issues with the reliability, equipment cost, wear and as well as the increased cost and maintenance of such moving parts.
Further, such methods limit the potential to harvest the full power potentially availed from the wind, and result in a compromise at which potentially lower but still useful power is not used when the wind speed is too low, and higher power is given up for those opportunities with higher than average wind speeds.
Hence, ideal locations for wind turbines are sites at which the wind constantly blows at a high speed, without significant lulls, or speed variations.
These compromises generally lead to the establishment of large scale turbine wind farms at limited location that generally have a high constant wind speed, and hence preclude a more economic generation of power for local user needs, which avoids the investment in a large transmission line infrastructure.
Accordingly, it would be advantageous to provide as a first object of this invention a means for direct transmission or AC generator power to an AC grid without intermediate DC conversion.
It is hence another object of the invention to achieve such direct conversion without a mechanical transmission and without compromising the energy potential of a particular wind turbine site to a fixed wind speed.